In general, dispensing a foamed material is desirable where it is necessary to dispense a material but where as little dispensing material as possible is to be applied for reasons of cost or weight, for example, but without the thickness of the coating being less than a certain value. Foamed materials are dispensed, in particular, in industrial applications in which the aim is to glue together two substrates or components, but by using as little adhesive as possible in order to reduce the amount of costly adhesive consumed and to minimize the increase in weight of the glued substrates or products due to such gluing.
If uniform gluing is to be achieved, it is necessary to dispense the foamed material as uniformly as possible. Uniform dispensing is understood in this context to mean that the material may be dispensed along a precisely predetermined contour with regard to the edges of the applied coating in the longitudinal direction and direction of width, on the one hand, and on the other hand that the thickness of the applied coating correspond with as much precision as possible over the entire coating region to a predetermined contour of coating thickness, in particular that it run as uniformly as possible in the longitudinal direction and the direction of the width, and particularly that the same thickness prevail at each point of the dispensed coating.
Methods are known from DE 197 57 237 and DE 197 57 238 in which a mixture of gas and adhesive is dispensed from an exit opening onto a substrate in order to apply the coating. The mixture of gas and adhesive is previously generated in a mixing device and conveyed by means of a pump to the exit opening. One specific problem encountered when foamed material is applied in this way is that variations arise when conveying the foamed material and that, as a result, the desired uniformity of applied coating is not ensured in all forms of application and differently dimensioned variants of the coating. Particularly when foamed coatings having a large width are to be applied, for example a width of more than half a meter, in particular more than one meter, a coating is produced with the known method that is subject to substantial local variations, with the result that the quality of coatings and hence the quality of an adhesive bond obtained by means of the coating is not sufficient for many applications.